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2 1. Spinal Cord Extends from the foramen magnum of the skull to thefirst or second lumbar vertebra(L1& L2)31 pairs of spinal nerves arise from the spinal cordCauda equina is a collection of spinal nerves at the inferior endThe cord does not extend the entire length of the vertebral column – so a group of nerves leaves the inferior spinal cord and extends downward. It resembles a horses tail and is called the cauda equina

13 Spinal NervesThere is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairsFormed by the combination of the ventral and dorsal roots of the spinal cordNamed for the region from which they ariseFigure 7.25a

14 5.Anatomy of Spinal NervesSpinal nerves divide soon after leaving the spinal cordDorsal rami—serve the skin and muscles of the posterior trunkVentral rami—form a complex of networks (plexus) for the anterior

15 5.& 7. Plexuses Sacral PlexusPlexus- ventral rami C1-T1 and T12-S4 branch extensively and join one another lateral to the vertebral column forming complicated nerve plexuses that serve motor and sensory needs***Except for T2 to T12,Ventral Rami from C1- T1 form Cervical & Brachial plexusesVentral rami from L1-S4 form Lumbar and Sacral plexuses6. Serve motor and sensory needs of the limbsVentral rami from T2-T12 do not form plexuses..they serve the muscles of intercostal spaces and the skin and muscles of the anterior and lateral trunkSacral Plexus

16 This diagram shows the nerves leaving from the vertebral canalNote: There are 7 cervical vertebrae but 8 pairs of cervical nerves.C1 – C7 emerge above the vertebrae for which they are named.C8 emerges between C7 and T1.The remaining spinal nerve pairs emerge below the same numbered vertebra.

17 PNS: The Spinal NervesLook how the dorsal and ventral roots merge to form the spinal nerve then split again to form the ventral and dorsal ramiFigure 7.25b

30 Spinal CordFunctions to transmit messages to and from the brain (white matter) and to serve as a reflex center (gray matter).extends about 17”diameter of your thumbThicker at the neck and end of the cord (cervical and lumbar enlargements) b/c of the large group of nerves connecting these regions of the cord w/ the arms and legs.

31 Spinal CordThe cord does not extend the entire length of the vertebral column – so a group of nerves leaves the inferior spinal cord and extends downward. It resembles a horses tail and is called the cauda equina.

32 Spinal Cord Notice the gross features of the spinal cord on the right.31 pairs of spinal nerves attach to the cord by paired roots and exit from the vertebral canal via the intervertebral foramina.

33 Cross Sectional Anatomy of the Spinal CordFlattened from front to back.Anterior median fissure and posterior median sulcus partially divide it into left and right halves.Gray matter is in the core of the cord and surrounded by white matter.

34 Resembles a butterfly.2 lateral gray masses connected by the graycommissure.Posterior projections are the posterior or dorsal horns.Anterior projections are the anterior or ventral horns.In the thoracic and lumbar cord, there also exist lateral horns.

35 Gray Matter Posterior horns contain interneurons.Anterior horns contain someinterneurons as well as the cellbodies of motor neurons.These cell bodies project their axons via the ventral roots of the spinal cord to the skeletal muscles.The amount of ventral gray matter at a given level of the spinal cord is proportional to the amount of skeletal muscle innervated.

36 Gray MatterLateral horn neurons are sympathetic motor neurons serving visceral organs.Their axons also exit via the ventral root.Afferent sensory fibers carrying info from peripheral receptors form the dorsal roots of the spinal cord. The somata of these sensory fibers are found in an enlargement known as a dorsal root ganglion.The dorsal and ventral roots fuse to form spinal nerves.

37 White Matter Myelinated nerve fibers.Allows for communication btwn the brain and spinal cord or btwn different regions of the spinal cord.White matter on each side of the cord is divided into columns or funiculi.Typically, they are ascending or descending.What does that mean?

38 Spinal NervesThe 2 roots join to form a spinal nerve prior to exiting the vertebral column.Roots are short and horizontal in the cervical and thoracic regions while they are longer and more horizontal in the sacral and lumbar regions.Almost immediately after emerging from its intervertebral foramen, a spinal nerve will divide into a dorsal ramus, a ventral ramus, and a meningeal branch that reenters and innervates the meninges and associated blood vessels.

39 Each ramus is mixed.Joined to the base of the ventral rami of spinal nerves in the thoracic region are the rami communicantes.Dorsal rami supply the posterior body trunk whereas the thicker ventral rami supply the rest of the body trunk and the limbs.